fix(mem0-plugin): fix 3 critical + 5 important issues from review

Critical fixes:
- C1: Pin/dream update_memory now reads content first via get_memory
  before updating, preventing metadata-only calls that wipe content
- C2: SessionStart memory count uses GET /v3/memories/?page_size=1 for
  real count from pagination envelope instead of search limit=100
- C3: on_task_completed.sh uses ${MEM0_PROJECT_ID:-unknown} to avoid
  crash when identity resolution fails under set -u

Important fixes:
- I1: session_stats.py tracks recent_ids (memory IDs + timestamps) for
  /mem0:forget undo support. Capped at 50 entries.
- I2: /mem0:health --deep mode adds memory quality analysis: duplicate
  detection, stale entry scan, contradiction flags, orphan tagging
- I3: /mem0:stats ASCII histogram for category distribution with bar
  chart, sorted by count descending
- I4: mem0-mcp skill documents access counter pattern: get_memory then
  update_memory to track which memories are actually used
- I5: on_pre_commit.py reads COMMIT_EDITMSG first (current commit),
  falls back to HEAD only if EDITMSG unavailable

Tests: 91 -> 94 (3 new for recent_ids tracking)

mem0-plugin/skills/mem0-dream/SKILL.md

@@ -183,7 +183,9 @@ For each approved merge pair:
 
 For each resolved conflict where the user chose A or B:
 - Identify the loser (the non-chosen memory).
-- `update_memory(<loser_id>, data={"metadata": {"confidence": 0.1, "superseded_by": "<winner_id>", "source": "mem0-dream"}})`
+- First call `get_memory(<loser_id>)` to read its current text content.
+- Then call `update_memory(<loser_id>, data=<original_text_content>)` to preserve the text while updating it.
+- **Important:** `update_memory` requires the `data` (text) parameter. A metadata-only call may error or wipe the content. Always read first, then update with the original text.
 
 Contradictions where the user chose `skip` are left untouched.